1. FIELD OF THE INVENTION
The present invention relates to a novel aromatic hetero ring-containing polyimide having a high modulus of elasticity and excellent heat resistance, and a composite thereof. More particularly, it relates to an aromatic heterocyclic polyimide containing a benzobisazole structure in the main chain and a composite thereof.
2. DISCUSSION OF BACKGROUND
Aromatic heterocyclic polymers are expected to be prospective materials having high strength, high modulus of elasticity and high heat resistance, but they are still at a stage of research and development except for polyimides and polybenzoimidazoles. Among them, poly-p-phenylenebenzobisthiazole (PBT) known as a fiber of higher modulus of elasticity is a rigid chain polymer obtainable by reacting 2,5-diaminobenzene-1,4-dithiol dihydrochloride with terephthalic acid in polyphosphoric acid at a high temperature of from 160.degree. to 200.degree. C. for a long period of time, and it presents a tensile modulus of elasticity (310 GPa) as high as at least twice that of poly-p-phenyleneterephthalamide (PPTA) (Kebler.RTM.) which is one of wholly aromatic polyamides. However, PBT is insoluble in any solvent except for a strong acid such as methanesulfonic acid or chlorosulfonic acid. Such acid solvents are highly corrosive to apparatus, and PBT is industrially disadvantageous in this respect.
On the other hand, an attention has been drawn to a development of polymer composites i.e. an attempt to disperse a rigid chain polymer and a soft polymer to each other at a molecular level to obtain a material having a high modulus of elasticity while effectively utilizing the rigidity of the rigid chain polymer. (Publication No. 50440/1980 of Japanese translation of a PCT application) However, the above-mentioned rigid chain polymer forms liquid crystals in a solution and is likely to undergo phase separation when mixed with a soft polymer. At least it is required to have an extremely dilute solution (about 3% by weight) in order to obtain a uniformly mixed solution as a prerequisite for uniform dispersion. Yet, a highly corrosive solvent is still required, and it is thereby difficult to establish a treating method which is adequatly advantageous from the industrial standpoint.